1. Field of the Invention
The present invention relates to a segmental ultrasonic cleaning apparatus capable of removing scales and sludge in a heat exchanger using ultrasound waves and, more particularly, to a segmental ultrasonic cleaning apparatus configured to remove scales and/or sludge deposited on a top surface of a tube sheet, which supports tubes of a steam generator in a nuclear power plant, through concentration of ultrasound energy on the top surface of the tube sheet.
2. Description of the Related Art
Typically, scales and/or sludge are deposited on a tube surface and a tube sheet supporting tubes of a commercial heat exchanger during heat exchange, as is known in the art. Particularly, despite continuous management of quality of reactor water flowing into a steam generator in a nuclear power plant, metallic scales and/or sludge are deposited in the steam generator, thereby causing deterioration in heat exchange efficiency affecting output of the nuclear power plant as well as corrosion of the steam generator which results in a reduction of the life cycle of the steam generator.
Therefore, for the nuclear power plant, it is necessary to perform periodic cleaning of the steam generator. Currently, the cleaning method for the steam generator is generally classified into chemical cleaning and high-pressure water jet cleaning. Chemical cleaning permits cleaning of the entirety of the steam generator. However, since chemical cleaning entails considerable cleaning costs and causes chemical damage to the steam generator in addition to consuming large amounts of water, the chemical cleaning is performed only when necessary. On the other hand, high-pressure water jet cleaning is performed once per scheduled overhaul to remove scales and/or sludge deposited on top of a tube sheet in the steam generator. However, the high-pressure water jet cleaning typically permits cleaning of only a region that high-pressure jet water can reach. For example, a steam generator of a Korean standard nuclear power plant includes more tubes than other types of steam generators, such that a distance between the tubes is very narrow, thereby forming a shadow zone which some of the high-pressure water cannot reach during high-pressure water jet cleaning, thereby deteriorating cleaning efficiency.
In the nuclear power plant, ultrasonic elements are often used to clean the steam generator. In this case, with the steam generator filled with water or a liquid cleaning agent, the ultrasonic elements are immersed therein to remove scales and/or sludge from the top surface of the tube sheet via ultrasonication. Typically, due to the characteristics of ultrasound waves, the ultrasound waves are propagated to a portion contacting the liquid. Thus, when using the ultrasonic elements to clean the steam generator, there is a problem in that the range of the ultrasound waves is increased but the energy density of the ultrasound waves is significantly lowered as the distance from a source of the ultrasound waves increases.